Problem: Omar is 3 times as old as Stephanie. Sixteen years ago, Omar was 7 times as old as Stephanie. How old is Omar now?
Solution: We can use the given information to write down two equations that describe the ages of Omar and Stephanie. Let Omar's current age be $o$ and Stephanie's current age be $s$ The information in the first sentence can be expressed in the following equation: $o = 3s$ Sixteen years ago, Omar was $o - 16$ years old, and Stephanie was $s - 16$ years old. The information in the second sentence can be expressed in the following equation: $o - 16 = 7(s - 16)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $o$ , it might be easiest to solve our first equation for $s$ and substitute it into our second equation. Solving our first equation for $s$ , we get: $s = o / 3$ . Substituting this into our second equation, we get: $o - 16 = 7($ $(o / 3)$ $- 16)$ which combines the information about $o$ from both of our original equations. Simplifying the right side of this equation, we get: $o - 16 = \dfrac{7}{3} o - 112$ Solving for $o$ , we get: $\dfrac{4}{3} o = 96$ $o = \dfrac{3}{4} \cdot 96 = 72$.